Many types of suspensions and supports include a spring and a damping device to help isolate that supported from the support structure or surface. For example, automotive vehicles commonly use separate springs and simple shock absorbers to support the vehicle frame on the axle assemblies. Simple shock absorbers are typically oil-filled cylinders within which a vented piston is mounted. The piston is connected to a shaft which extends out of one end of the cylinder. The outer end of the shaft is mounted to one point on the vehicle and the other end of the cylinder is mounted to another point on the vehicle in parallel with the suspension spring. Thus, simple shock absorbers only provide damping and not support.
Another type of shock absorber, which is the type commonly used with motorcycles, off-road vehicles, competition automotive vehicles and off-road bicycles, combines both the suspension function and the shock absorbing function in one unit. This second type of shock absorber commonly uses a spring unit to provide the suspension function coupled with a damping unit to provide the damping function. Conventional shock absorber designs commonly incorporate an external coil spring, an internal air spring, or an internal bladder to provide the suspension function.
Typical shock absorbers (also referred to as shocks) provide two kinds of damping: compression damping (“CD”), and rebound damping (“RD”). One refers to damping force created during “inward” travel of the shaft (shortening of the shock), the other refers to force created during “outward” travel of the shaft (lengthening of the shock). Generally, but not always—depending on linkage connecting shock to vehicle, RD applies during outward motion and CD applies during inward motion. Some shocks are externally adjustable by the user to provide for RD and/or CD adjustment.
Piston-type shock absorbers can be designed to provide the same amount of damping on both the compression stroke and the rebound stroke. Alternatively, the fluid passageways through the vented, damping piston can be designed so that the restriction to fluid flow through the damping piston during the compression stroke is different from the restriction to fluid flow during the rebound stroke. In this case the damping during the entire compression stroke is different from the damping during the entire stroke.
Another type of damping is called position-sensitive damping. Position-sensitive damping is typically achieved by the combination of conventional vented piston damping, with the oil flowing through the damping system, plus damping provided by the passage of oil around the damping piston through a bypass chamber or channel, which permits oil to bypass the piston during part of the piston stroke. The bypass channel permits lesser damping over the portion of the stroke during which some fluid flows around the piston through the bypass channel. Therefore, the shock can have different damping characteristics along different segments of the stroke. This is beneficial to the user because a single set of shocks can provide a smooth damping for less aggressive riding and firm damping for aggressive riding without making any adjustments during the ride. For example, the shocks can provide reduced damping in the mid-stroke zone, where the shock is most active in, for example, trail riding or other less aggressive riding. If the rider starts riding more aggressively, or hits a large bump, causing the shock to compress deeper into the stroke, the bypass damping then becomes available and the shock also relies on the conventional piston damping. This type of shock absorber has been available for many years.
U.S. Pat. No. 5,178,239 illustrates another example of a position-sensitive shock absorber. The position-sensitive damping action of the bypass channel is available during both the compression and rebound strokes. U.S. Pat. No. 6,415,895 is directed to shock absorbers, including position-sensitive shock absorbers in which the position-sensitive damping can be different during compression and rebound strokes and shock absorbers with damping adjusters which vary the damping provided during compression and rebound strokes. A further aspect is directed to a shock absorber including a cylinder with a piston moveably mounted within the cylinder.
It is an object of the invention to provide a novel shock absorber that provides both a suspension function and a damping function.
It is also an object of the invention to provide a novel shock absorber that has bypass passageways whose hydraulic fluid flow can be increased or decreased by external mechanical structure to vary the damping characteristics.
It is another object of the invention to provide a novel shock absorber that has bypass tubes having a kidney-shaped transverse cross section.
It is an additional object of the invention to provide a novel shock absorber that has unique check valves having kidney-shaped check valve pistons.
It is also an object of the invention to provide a novel shock absorber that has structure for increasing or decreasing the length of the external coil spring.